Apparatus and method for measuring chuck attachment force

ABSTRACT

An apparatus and method for measuring a chuck attachment force are provided. The apparatus is capable of measuring loads applied to a measurement substrate, while the measurement substrate is detached from a chuck, and precisely calculating necessary force through a process of comparing and analyzing values of the measured loads. This may prevent errors in the application of attachment force during a semiconductor manufacturing process. In the semiconductor manufacturing process, when the substrate is detached from a chuck, the substrate may be prevented from being deformed or cracked.

BACKGROUND

1. Field

An apparatus and method for measuring chuck attachment force aredisclosed herein.

2. Background

Apparatus and method for measuring chuck attachment force are known.However, they suffer from various disadvantages.

BRIEF DESCRIPTION OF THE DRAWINGS

Embodiments will be described in detail with reference to the followingdrawings in which like reference numerals refer to like elements, andwherein:

FIG. 1 is a schematic diagram of an apparatus for measuringelectrostatic force according to an embodiment;

FIG. 2 is a flow chart of a method of measuring electrostatic forceaccording to an embodiment;

FIG. 3 is a schematic diagram of an apparatus for measuringelectrostatic force according to another embodiment;

FIG. 4 is a bottom view of the electrostatic force measuring apparatusof FIG. 3;

FIGS. 5 and 6 are views illustrating operation of the electrostaticforce measuring apparatus of FIG. 3;

FIG. 7 is a flow chart of a method of measuring electrostatic forceaccording to another embodiment;

FIG. 8 is a schematic diagram of an apparatus for measuringelectrostatic force according to another embodiment;

FIG. 9 is a block diagram of a load measuring device of FIG. 8;

FIGS. 10 and 11 are views illustrating operation of the electrostaticforce measuring apparatus of FIG. 8; and

FIG. 12 is a flow chart of a method of measuring electrostatic forceaccording to another embodiment.

DETAILED DESCRIPTION

Embodiments disclosed herein are directed to an apparatus and method formeasuring chuck attachment force. Certain embodiments are disclosedemploying an electrostatic chuck and measuring electrostatic force.However, the apparatus and method may be utilized with other types ofchucks, such as a vacuum chuck, and to measure other types of forces,such as a vacuum force. Further, features of each of the disclosedembodiments may be utilized with any of the other embodiments as desiredbased on, for example, the desired application.

Generally, in processes of treating substrates, such as semiconductorwafers, thin film transistors (TFTs) used in flat panel displays, glasssubstrates or similar devices, the substrates, which are carried intochambers, are moved to desired positions, dropped onto support surfaces,and thereafter, are arranged. Recently, according to the integration andlightness of circuits in the semiconductor field, and according to theincrease in display area in the field of manufacturing flat paneldisplays, the significance of a technique of holding substrates toarrange the substrates and drop the substrates at desired positions hasbeen emphasized.

As representative examples of such substrate holding techniques, thereare a method using a clamp, a method using vacuum force, and a methodusing an electrostatic chuck (ESC). In the method using the clamp, asubstrate is fixed by clamping an edge of the substrate using the clamp.The clamp may be made of ceramic or other material. In the method usingthe electrostatic chuck, the electrostatic chuck adsorbs and holds asubstrate using electrostatic force generated at contact surfacesbetween the electrostatic chuck and the substrate.

Recently, of such substrate holding methods, application of the methodusing the electrostatic chuck, which enhances uniformity of themanufacturing process, has increased. A representative example ofrelated art pertaining to an electrostatic chuck was disclosed in U.S.Pat. No. 6,134,096, entitled “ELECTROSTATIC CHUCK”. In this patent, theelectrostatic chuck has a structure including an insulation layer, anelectrode layer, and a dielectric layer, and is constructed such that asubstrate is attached to the electrostatic chuck by applying power of−1000V to +1000V to the electrostatic chuck. In the case of the methodof holding the substrate using the electrostatic chuck, because thechuck holds the substrate by adsorbing it using electrostatic force,various operations may be stably conducted during a semiconductormanufacturing process, thus preventing the substrate from being damagedand reducing the defective proportion of products.

The electrostatic chuck for adsorbing and holding the substrate usingelectrostatic force may include a base plate, which may be made ofceramic, an electrode, which may be provided on the base plate, and adielectric, which may be supplied with power through the electrode.

In the electrostatic chuck, when power is applied to the electrode toadsorb the substrate, the surfaces of the substrate and the electrodemay be polarized. At this time, electrostatic force is generated on theelectrostatic chuck, by which the electrostatic chuck adsorbs and holdsthe substrate.

Recently, according to an increase in the area of flat panel displays,such an electrostatic chuck may include a plurality of dielectrics,which may be provided on a base plate and adsorb a substrate. Theplurality of dielectrics, which adsorb and hold the substrate, mustensure even electrostatic force.

Electrostatic force may be set depending on a material and thickness ofthe substrate. If the dielectrics do not ensure even electrostaticforce, an error of electrostatic force may occur, so that, when thesubstrate is detached from the electrostatic chuck, the substrate maynot be correctly detached from the electrostatic chuck, and a stickingphenomenon, in which the substrate may snap back onto the electrostaticchuck, may be induced. Further, the substrate may be deformed orcracked. Therefore, a problem of reduced manufacturing efficiencyresults.

As shown in FIG. 1, an electrostatic force measuring apparatus 10according to an embodiment may include an electrostatic chuck 100, ontowhich a measurement substrate S may be seated, a power supply device 150that applies voltage to the electrostatic chuck 100, and a separatingdevice 120 that detaches the measurement substrate S from theelectrostatic chuck 100 to which voltage is applied. The electrostaticforce measuring apparatus 10 may further include a variable loadapplying device 110, which may be connected to the separating device 120and operate the separating device 120 through a process of changing aload thereon, and a controller 160 that measures the load of thevariable load applying device 110 when the measurement substrate S isattached to the separating device 120 and measures the load of thevariable load applying device 110 when the measurement substrate S isdetached from the electrostatic chuck 100, thus calculating theelectrostatic force using a change in the load of the variable loadapplying device 110.

The electrostatic chuck 100 absorbs the measurement substrate S usingelectrostatic force generated by a polarization phenomenon occurring onsurfaces between the measurement substrate S and the electrostatic chuck300 when power is applied thereto. A dummy substrate that meets the sameconditions as a thin film transistor and a glass substrate ofsemiconductor water of flat panel display may be used as the measurementsubstrate S. In addition, a separate chuck carrying device and aseparate substrate carrying device may be provided to move the chuck 300and the substrate S, although not shown in the drawings.

The electrostatic chuck 100 may be supported by a support device 150.The support device 150 may include a support plate or stage 151 andsupport legs 153 and may be charged by voltage applied from the powersupply device 155. The support plate 151 may serve to hold theelectrostatic chuck 100, on which the measurement substrate S is loaded.When voltage is applied from the power supply device 155 to theelectrostatic chuck 100, electric charges having a polarity opposite tothat of the electric charges applied to the electrostatic chuck 100 maybe induced at a contact surface between the electrostatic chuck 100 andthe measurement substrate S, so that induced electromotive force may begenerated by the induced electric charges, by which the measurementsubstrate S may be attached to the electrostatic chuck 100.

The electrostatic chuck 100 may have a dielectric ceramic coating layerbetween it and the measurement substrate S. Depending on a thickness ofthe dielectric ceramic coating layer, the attaching force with which themeasurement substrate S may be chucked to the electrostatic chuck 100may be changed.

Further, one or more sensor(s) 102 that detect whether the measurementsubstrate S is attached to or detached from the electrostatic chuck 100may be provided in the surface of the electrostatic chuck 100 thatcontacts the measurement substrate S. The sensor(s) 102 may comprise apressure sensor that detects a change in pressure, or a magnetic sensorthat detects a change in the magnetic field between the measurementsubstrate S and the electrostatic chuck 100.

The power supply device may include a direct current generator (notshown) that supplies direct current to the electrostatic chuck 100. Theseparating device 120 may include a vacuum device 130 that creates avacuum to adsorb the measurement substrate S, and a drive device 140that transmits power to move the vacuum device 130. The vacuum device130 may include a vacuum suction device 131 a having vacuum suctionmembers 131 b that adsorb the measurement substrate S, a vacuum pump 132that suctions air through the vacuum suction members 131 b, and a vacuumpipe 133, which may be connected between the vacuum suction members 131b and the vacuum pump 132. Vacuum suction pads, which may be made ofrubber, or vacuum suction pins, which may be made of a ceramicnonconductor, may be used as the vacuum suction members 131 b to preventthe vacuum suction member 131 b from affecting the electrostatic forcegenerated between the measurement substrate S and the electrostaticchuck 100.

The vacuum pump 132 suctions air through the vacuum suction members 131b to attach the measurement substrate S to the vacuum suction device131a, such that, when the measurement substrate S is detached from theelectrostatic chuck 100, the measurement substrate S, which may beadsorbed by the vacuum suction members 131 b, may be moved along withthe vacuum suction device 131 a in a vertical direction. As set forthabove, the vacuum pipe 133 may serve to connect the vacuum suctiondevice 131 a and the vacuum pump 132 to each other.

The drive device 140 may include at least one, or, in the example ofthis embodiment, two pulleys 141 and 142, and a power transmittingmember 143, which may be coupled to the pulleys 141 and 142 and thevacuum suction member 131 to conduct a power transmitting function. Inthis embodiment, the pulleys 141 and 142 include a first pulley 141 anda second pulley 142. The first pulley 141 may support the powertransmitting member 143, which may be connected to the vacuum suctiondevice 131 a, such that the power transmitting member 143 may pull thevacuum suction device 131 a and the measurement substrate S adsorbed andheld by the vacuum suction members 131 b with force corresponding totension applied to the power transmitting member 143 by the variableload applying device 110.

Further, the second pulley 142 may also serve to support the powertransmitting member 143 along with the first pulley 141 such that theforce applied from the variable load applying device 110 may betransmitted to the measurement substrate S, attached to theelectrostatic chuck 100, through the power transmitting member 143, thedirection of which may be changed by the first and second pulleys 141and 142. A stationary pulley or a movable pulley may be used as each ofthe first and second pulleys 141 and 142. Further, a plurality ofpulleys may be used to change the direction in which force istransmitted.

The power transmitting member 143 may connect the vacuum suction device131 a, the first pulley 141, the second pulley 142, and the variableload applying device 110 to each other and transmit force, generated bythe variable load applying device 110, to the vacuum suction device 131a. A wire rope or a chain, which may be capable of withstanding a loadof several tons, may be used as the power transmitting member 143.

In the separating device 120 having the above-mentioned construction,the vacuum device 130 creates a vacuum, thereby adsorbing themeasurement substrate S, and the drive device 140 moves the vacuumsuction device 131 a, thus detaching the measurement substrate S fromthe electrostatic chuck 100.

The variable load applying device 110 adjusts the load thereof inresponse to an intensity of electrostatic force applied between themeasurement substrate S and the electrostatic chuck 100. That is, theforce generated in the variable load applying device 110 may beproportional to the intensity of the electrostatic force. The loadchanging operation of the variable load applying device 110 may beconducted by a method in which one weight may be replaced with anotherusing a separate machine, or by a method in which the load may beincreased or reduced using a vertical load cylinder.

The controller 160 may receive, from the sensor(s) 102, informationabout whether the measurement substrate S is detached from theelectrostatic chuck 100. Also, the controller 160 may adjust the load ofthe variable load applying device 110 until the measurement substrate Sis detached from the electrostatic chuck 100, and measure the load ofthe variable load applying device 110 when the measurement substrate Sis detached from the electrostatic chuck 100. In addition, thecontroller 160 may serve to calculate the electrostatic force using themeasured load of the variable load applying device 110.

The operation of the electrostatic force measuring apparatus accordingto the above-described embodiment, having the above-mentionedconstruction, will be described herein below.

As shown in FIG. 2, the measurement substrate S, which may be adsorbedby the vacuum suction members 131 b, may be seated on the electrostaticchuck 100, in step S110. Thereafter, when voltage is applied from thepower supply device 155 to the electrostatic chuck 100, theelectrostatic chuck 100 may be charged, and electrostatic forcegenerated between the measurement substrate S and the electrostaticchuck 100. Then, the measurement substrate S may be attached to theelectrostatic chuck 100 by the electrostatic force, in step S120.

After the measurement substrate S has been attached to the electrostaticchuck 100, the controller 160 may gradually increase the load of thevariable load applying device 110 until the measurement substrate S isdetached from the electrostatic chuck 100, in step S130. Then, thetension of the power transmitting member 143, which may be coupled tothe variable load applying device 110, may be gradually increased, andpulling force may be applied to the vacuum suction members 131 b. Theforce by which the vacuum suction members 131 b adsorb the measurementsubstrate S must be greater than the electrostatic force between theelectrostatic chuck 100 and the measurement substrate S to make itpossible to detach the measurement substrate S from the electrostaticchuck 100.

The load of the variable load applying device 110 may be increased untilthe measurement substrate S is detached from the electrostatic chuck100. When the measurement substrate S is detached from the electrostaticchuck 100, the sensor(s) 102, which may be provided in the electrostaticchuck 100, may detect the detachment of the measurement substrate S fromthe electrostatic chuck 100, in step S140. The detected information ofthe sensor(s) 102 may be transmitted to the controller 160, so that aload of the variable load applying device 110 when the measurementsubstrate S is detached from the electrostatic chuck 100 may bedetermined, in step S150.

Subsequently, the difference between the load of the variable loadapplying device 110 when the measurement substrate S is attached to thevacuum suction members 131 b and the load of the variable load applyingdevice 110 when the measurement substrate S is detached from theelectrostatic chuck 100 may be calculated, and the exact value ofelectrostatic force from this difference value may be determined, instep S160.

In the above-described electrostatic force measuring apparatus andmethod of measuring electrostatic force, an exact value of electrostaticforce may be determined from the difference between the load of thevariable load applying device 110 when the measurement substrate S isattached to the vacuum suction members 131 b and the load of thevariable load applying device 110 when the measurement substrate S isdetached from the electrostatic chuck 100, thus preventing an error inthe application of electrostatic force in a semiconductor manufacturingprocess, and preventing a substrate from being cracked or damaged whenit is detached from an electrostatic chuck in the semiconductormanufacturing process.

Hereinafter, an apparatus for measuring electrostatic force and a methodof measuring electrostatic force according to additional embodimentswill be described in detail with reference to FIGS. 3 and 7.

As shown in FIG. 3, the electrostatic force measuring apparatus 20according to this embodiment may include an electrostatic chuck 200,onto which a measurement substrate S may be seated, a power supplydevice 255 that applies voltage to the electrostatic chuck 200, and aseparating device 220 that detaches the measurement substrate S from theelectrostatic chuck 200 to which voltage is applied. The electrostaticforce measuring apparatus 20 may further include variable load applyingdevices 210, which may be connected to the separating device 220 andoperate the separating device 220 through a process of changing a loadthereof, and a controller 260 that measures the load of the variableload applying devices 210 when the measurement substrate S is attachedto the separating device 220 and measures the load of the variable loadapplying devices 210 when the measurement substrate S is detached fromthe electrostatic chuck 200, thus calculating electrostatic force usinga change in the load of the variable load applying devices 210.

The electrostatic chuck 200 absorbs the measurement substrate S usingelectrostatic force generated by a polarization phenomenon occurring onsurfaces between the measurement substrate S and the electrostatic chuck200 when power is applied thereto. A dummy substrate that meets the sameconditions as a thin film transistor and a glass substrate ofsemiconductor water of flat panel display may be used as the measurementsubstrate S. In addition, a separate chuck carrying device and aseparate substrate carrying device may be provided to move the chuck 200and the substrate S, although not shown in the drawings.

The electrostatic chuck 200 may be supported by a support device 250.The support device 250 may include a support plate or stage 251 andsupport legs 253. A through hole 236 a may be formed in the supportplate 251, and a plurality of holes 203 may be formed through theelectrostatic chuck 200. The electrostatic chuck 200 may be made ofceramic and may have a ceramic coating layer between the measurementsubstrate S and the electrostatic chuck 200. The ceramic coating layermay provide elasticity when the measurement substrate S is attached tothe electrostatic chuck 200, thus increasing attachment abilitytherebetween.

Further, one or more sensor(s) 202 that detect whether the measurementsubstrate S is attached to or detached from the electrostatic chuck 200may be provided in a surface of the electrostatic chuck 200 thatcontacts the measurement substrate S. When the measurement substrate Sis detached from the electrostatic chuck 200, the sensor(s) 202 maydetect and transmit a signal(s) to the controller 260. The sensor(s) 202may include a pressure sensor or a magnetic sensor. The power supplydevice 255 may include a direct current generator (not shown) thatsupplies direct current to the electrostatic chuck 200.

The separating device 220 may include a lift device 230 that moves themeasurement substrate S upwards, and a drive device 240 that transmitspower to operate the lift device 230. The lift device 230 may include aplurality of lift pins 231, which may be brought into contact with themeasurement substrate S through the holes 203 formed through theelectrostatic chuck 200, a lift plate 232, which may be coupled to thelift pins 231, a lift shaft 233, which may extend from the lift plate232 to transmit power from the drive device 240 to the lift plate 232,and guide bars 234, which may be provided between the support plate 251and the lift plate 232 to guide the movement of the lift plate 232.

When voltage is applied from the power supply device 255 to theelectrostatic chuck 200, electric charges having a polarity opposite tothat of the electric charges applied to the electrostatic chuck 200 areinduced on a surface of the measurement substrate S that contacts theelectrostatic chuck 200. If the lift pins 231, which may be made of aconductor, are used, when the lift pins 231 contact the measurementsubstrate S to detach the measurement substrate S from the electrostaticchuck 200, electric charges of the measurement substrate S may bedischarged through the lift pins 231, so that the electrostatic forcemay not be precisely measured. Thus, the lift pins 231 may benonconductors made, for example, of ceramic material to prevent thedischarge of electric charges of the measurement substrate S.

Further, in this embodiment, the measurement substrate S may be detachedfrom the electrostatic chuck 200 by applying a pushing force to the liftpins 231, which may be in a state of contact with the measurementsubstrate S, so that the attractive force between the electrostaticchuck 100 and the measurement substrate S, that is, the electrostaticforce therebetween, may be measured. Therefore, to precisely measureelectrostatic force, contact detecting sensors 235, which may detectwhether the lift pins 231 are brought into contact with the measurementsubstrate S, may be provided on ends of the lift pins 231 that contactthe measurement substrate S.

The lift plate 232 may serve to transmit force from the drive device 240to the measurement substrate S and may vertically move along the guidebars 234. That is, the lift pins 231 may transmit force to themeasurement substrate S using upward movement of the lift plate 232 suchthat the measurement substrate S may be detached from the electrostaticchuck 100. The lift pins 231 may be provided on an upper surface of thelift plate 232, and the lift shaft 233 may be coupled at a centralportion to a lower surface of the lift plate 232. The lift shaft 233 mayserve to transmit the force of the drive device 240 to the lift plate232 and to maintain a horizontally leveled state of the lift plate 232along with the guide bars 234.

The guide bars 234 may serve to maintain the lift plate 232 in thehorizontally leveled state such that several lift pins 231 may evenlytransmit force, which may be applied from the drive device 240 to thelift plate 232, to the measurement substrate S. In addition, the guidebars 234 may serve to define a movement space 236 b such that the liftplate 232 may be vertically moved in the movement space 236 b. Further,a stop pin 237 may be provided in a lower end of each guide bar 234 toprevent the lift device 230 from being removed from the movement space236 b defined by the guide bars 234.

The drive device 240 may include at least one set of pulleys 241, andpower transmitting members 243, which may be connected to the pulleys241 and the lift shaft 233 to conduct a power transmitting function. Thepower transmitting members 243 may be coupled at first ends thereof to alower end of the lift shaft 233. Each power transmitting member 243 maybe coupled at a second end thereof to the corresponding variable loadapplying device 210. The upper end of the lift shaft 233 may be coupledto the central portion of the lift plate 232.

A stationary pulley may be used, for example, as each pulley 241, and awire rope or a chain, which is capable of withstanding a load of severaltons, may be used as each power transmitting member 243.

As shown in FIG. 4, in this embodiment, four power transmitting members243, each of which may be connected to the lift shaft 233, may beoriented in four respective directions and may be wrapped around therespective pulleys 241, which may be provided on four respective supportlegs 253. Further, the four pulleys 241 may be installed to maintainbalance of the lift device 230 and to disperse the force that is appliedto the lift device 230.

In the case of four pulleys 241, if the loads generated in the variableload applying devices 210 are equal to each other, the force applied tothe lift device 230 is four times as much as the force applied to eachpulley 241. Further, even if the loads generated in the variable loadapplying devices 210 differ from each other, the force applied to thelift device 230 is equal to the sum of the loads generated in thevariable load applying devices 210.

The loads of the variable load applying devices 210 may be controlled bythe controller 260. The vertical position of the lift device 230 may bechanged depending on the change in the load of the variable loadapplying devices 210.

When the load of the variable load applying devices 210, which may beconnected to respective power transmitting members 243, is increased, anupward moving force may be transmitted to the lift plate 232, coupled tothe lift shaft 233. Thereby, the lift plate 232 may be moved upwards.Here, as a modification of the method of vertically moving the liftplate 232, a lift cylinder may be used. Further, the load changingoperation of each variable load applying device 210 may be conductedusing counterbalances or using a vertical load cylinder.

The controller 260 may receive information about whether the lift pins231 have been brought into contact with the measurement substrate S,measure the load of the variable load applying devices 210 when the liftpins 231 have been brought into contact with the measurement substrateS, and increase the load of the variable load applying devices 210 untilthe measurement substrate S is detached from the electrostatic chuck200. Thereafter, the controller 260 may measure the load of the variableload applying devices 210 when it detects the detachment of themeasurement substrate S from the electrostatic chuck 200 using thesensor(s) 202.

Meanwhile, as shown in FIG. 5, in the drive device 240, which uses thepulleys 241, when the load of the variable load applying devices 210connected to the first ends of the respective power transmitting members243 is increased, the tension of the power transmitting member 243increases, and thus pulls the lift shaft 233. Thereby, the lift plate232 may be moved upwards.

However, if a distance between the measurement substrate S and the liftdevice 230 is relatively large, when detaching the measurement substrateS from the electrostatic chuck 200, because the force required formoving the lift device 230 to the measurement substrate S may also beincluded in the calculation of the load of the variable load applyingdevices 210, it is difficult to precisely measure electrostatic force.Therefore, as shown in FIG. 6, when the lift pins 231 are moved to thecontact surface of the measurement substrate S, the load of the liftdevice 230 may be measured, and when the measurement substrate S isdetached from the electrostatic chuck 200, the load of the lift device230 may be measured. Thereafter, electrostatic force may be calculatedusing the difference between the loads. Then, the electrostatic forcemay be measured more precisely.

The operation of the electrostatic force measuring apparatus accordingto this embodiment, having the above-mentioned construction, will bedescribed herein below.

As shown in FIG. 7, the measurement substrate S may be seated on theelectrostatic chuck 200, in step S210. Thereafter, when voltage isapplied from the power supply device 255 to the electrostatic chuck 200,the electrostatic chuck 200 may be charged, and electrostatic forcegenerated between the measurement substrate S and the electrostaticchuck 200. Then, the measurement substrate S may be attached to theelectrostatic chuck 200 by the electrostatic force, in step S220.

After the measurement substrate S has been attached to the electrostaticchuck 200, the controller 260 may gradually increase the load of thevariable load applying devices 210. Then, the tension of the powertransmitting members 243 connected to the respective variable loadapplying devices 210 may be gradually increased, so that the lift shaft233 may be pulled, by which the lift device 230 may be slowly movedupwards.

To reduce an error in the measurement of the electrostatic force, thelift device 230 may be first moved upwards until the lift pins 231 arebrought into contact with the measurement substrate S. When the liftpins 231 are brought into contact with the measurement substrate S, thecontact detecting sensors 235, which may be provided in the lift pins231, may detect the contact therebetween. At this time, the controller260 may measure the load of the variable load applying devices 210, instep S230. In the case where each variable load applying device 210 usesa method in which a load is varied by replacing a counterbalance withanother, the load may be a value resulting from multiplying the weightsof the counterbalances by the acceleration of gravity. This value may beequal to the force applied to the lift device 230.

The load of the variable load applying devices 210 may be graduallyincreased. Then, the lift device 230 may be moved further upwards.Ultimately, the measurement substrate S is detached from theelectrostatic chuck 200. As such, when the measurement substrate S isdetached from the electrostatic chuck 200, the sensor(s) 202 installedin the electrostatic chuck 200 may detect such detachment, in step S240.The detected information of the sensor(s) 202 may be transmitted to thecontroller 260, and the controller 260 may measure the load of thevariable load applying devices 210 when the measurement substrate S isdetached from the electrostatic chuck 200, in step S250.

Thereafter, electrostatic force may be precisely calculated using thedifference between the load of the variable load applying devices 210when the measurement substrate S is detached from the electrostaticchuck 200 and the load of the variable load applying devices 210 whenthe lift pins 235 are brought into contact with the measurementsubstrate S, in step S260.

In the above-described electrostatic force measuring apparatus andmethod of measuring electrostatic force, the exact value ofelectrostatic force may be determined from the difference between theload of the variable load applying devices 210 when the lift pins 235are brought into contact with the measurement substrate S and the loadof the variable load applying devices 210 when the measurement substrateS is detached from the electrostatic chuck 200, thus preventing an errorin the application of electrostatic force in a semiconductormanufacturing process, and preventing a substrate from being cracked ordamaged when it is detached from an electrostatic chuck in thesemiconductor manufacturing process.

Hereinafter, an apparatus for measuring electrostatic force and a methodof measuring electrostatic force according to additional embodimentswill be described in detail with reference to FIGS. 8 and 12.

As shown in FIG. 8, the electrostatic force measuring apparatus 30according to this embodiment may include an electrostatic chuck 300,onto which a measurement substrate S may be seated, and a separatingdevice 320 that detaches the measurement substrate S from theelectrostatic chuck 300. The electrostatic force measuring apparatus 30may further include a load measuring apparatus 310 that measures theload when the separating device 320 is brought into contact with themeasurement substrate S and measures the load when the measurementsubstrate S is detached from the electrostatic chuck 300.

The electrostatic chuck 300 may be supported by a support device 350.The support device 350 may include a stage 351, onto which theelectrostatic chuck 300 may be placed, and support frames 353, which maybe provided under a perimeter of a lower surface of the stage 351 tosupport the stage 351.

The electrostatic chuck 300 adsorbs the measurement substrate S usingelectrostatic force generated by a polarization phenomenon occurring onsurfaces between the measurement substrate S and the electrostatic chuck300 when power is applied thereto. A dummy substrate that meets the sameconditions as a thin film transistor and a glass substrate of asemiconductor wafer or a flat panel display may be used as themeasurement substrate S. In addition, a separate chuck carrying deviceand a separate substrate carrying device may be provided to move theelectrostatic chuck 300 and the substrate S, although not shown in thedrawings.

In detail, the electrostatic chuck 300 may be placed on an upper surfaceof the stage 351. An electrode (not shown) for applying power to theelectrostatic chuck 300 may be provided in the stage 351.

The separating device 320 may include a lift device 330, which may bedisposed below the stage 351 and push the substrate S to detach it fromthe electrostatic chuck 300, and a drive device 340 that verticallymoves the lift device 330. The lift device 330 may include a pluralityof lift pins 331, which may be vertically moved through the stage 351and the electrostatic chuck 300, a lift plate 332 that supports the liftpins 331, and guide bars 334, which may be provided between the supportdevice 350 and the lift plate 332 to guide the movement of the liftplate 332.

Here, the lift pins 331 and the lift plate 332 may be vertically movedunder guidance of the guide bars 334 in a state in which the lift plate332 is parallel to the substrate S attached to the electrostatic chuck300. Thus, the lift pins 331, which may be supported by the lift plate332, may evenly contact the substrate S, attached to the electrostaticchuck 300. Therefore, a measurement error by the load measuring device310 measuring a load may be reduced.

At least two guide bars 334 may be provided at respective oppositepositions under the perimeter of the stage 351. Further, a coupler 337,which is vertically movable along the corresponding guide bar 334, maybe provided on each lift plate 332. Alternatively, through holes (notshown) may be formed through the lift plate 332 such that the lift plate332 may be vertically movable along the guide bars 334 through thethrough holes.

Meanwhile, one or more sensor(s) 302 may be provided in the stage 351 todetect whether the substrate S is placed on the electrostatic chuck 300and whether the lift pins 331 are brought into contact with thesubstrate S. The sensor(s) 302 may be connected to the load measuringapparatus 310 to transmit information about placement of the substrate Sand contact between the lift pins 331 and the substrate S to the loadmeasuring device 310.

In detail, when the substrate S is placed on the electrostatic chuck300, the sensor(s) 302 may transmit information about the placement ofthe substrate S to the load measuring device 310. The load measuringapparatus 310 may measure a first load W1, which may be the load of thelift device 330 before it pushes the substrate S. Further, when the liftpins 331 are brought into contact with the substrate S, the sensor(s)302 may transmit information about the contact between the lift pins 331and the substrate S to the load measuring apparatus 310. The loadmeasuring device 310 may measure a second load W2, which may be the loadof the lift device 330 when the substrate S is detached from the chuck300.

Here, as shown in FIG. 8, the sensor(s) 302 may comprise a pair ofoptical sensors, which may face each other and be located on oppositesides of the measurement substrates. Alternatively, a pressure sensor ora magnetic sensor, which may be installed in an upper surface of thechuck 300, on which the measurement substrates is seated, may be used asthe sensor(s) 302, although not shown in the drawings.

The drive device 340 may include a lift screw 341, which may movevertically, and a power generating and transmitting device 342, whichmay be coupled to the lift screw 341 and supply power to vertically movethe lift screw 341. The lift screw 341 may be provided below the liftdevice 330 and may be constructed such that the lift plate 332 and thelift pins 331, which may be supported on the lift plate 332, may bevertically moved together with the vertical movement of the lift screw341.

The power generating and transmitting device 342 may include a powertransmitting screw 343, which may have a rotating shaft oriented in adirection perpendicular to the lift screw 341, a bevel gear 344, whichmay be provided in a junction between the lift screw 341 and the powertransmitting screw 343, and a power source 345, which may rotate thepower transmitting screw 343.

The power source 345 may be in the form of a manual handle so that powermay be supplied by rotating the handle using the manual power of a user.Alternatively, a mechanical power source, such as a drive motor, may beused to supply power.

The load measuring apparatus 310 may be disposed between the lift device330 and the drive device 340. The upper surface of the load measuringapparatus 310 may be in contact with the lower surface of the lift plate332, and the lower surface thereof may be coupled to the lift screw 341.

As shown in FIG. 9, the load measuring apparatus 310 may include a loadmeasuring device 311 that measures the first load W1 and the second loadW2, a memory 312 that stores the first load value W1 and the second loadvalue W2, an arithmetic device 313 that calculates a difference valuebetween the first load value W1 and the second load value W2, which maybe stored in the memory 312, and a display 314 that displays thedifference value.

Here, a typical electron scale may be used as the load measuring device311. Alternatively, a piezoelectric sensor, which uses the phenomenon inwhich, when mechanical force is applied to a substance made of materialsuch as ceramic, an internal stress is generated and electricpolarization is induced in the substance, may be used as the loadmeasuring device 311.

When the lift screw 341 is moved upwards to detach the substrate S fromthe electrostatic chuck 300, the pressure of the lift screw 341 may betransmitted to the load measuring apparatus 310. Then, the loadmeasuring apparatus 310 moves the lift plate 332 upwards using thepressure of the lift screw 341, by which the lift pins 331, which may besupported on the lift plate 332, may be moved upwards.

During this process, the load measuring device 311 measures both thepressure of the lift screw 341 that is applied to the lift device 330before the substrate S, attached to the chuck 300, is pushed by the liftpins 331, and the pressure of the lift screw 341 that is applied to thelift device 330 when the substrate S is detached from the chuck 300. Inother words, the load measuring device 311 measures both a first loadW1, which is the load of the lift device 330 before it pushes thesubstrate S attached to the chuck 300, and a second load W2, which isthe load of the lift device 330 when the substrate S is detached fromthe chuck 300.

The operation of the electrostatic force measuring apparatus accordingto this embodiment, having the above-mentioned construction will bedescribed herein below.

As shown in FIGS. 10 through 12, the electrostatic chuck 300 may befirst placed on the stage 351 of the support device 350, and thesubstrate S may be seated on the upper surface of the electrostaticchuck 300, in step S310. As such, when the electrostatic chuck 300 isplaced on the stage 351 of the support device 350 and the substrate S isseated on the electrostatic chuck 300, the sensor(s) 302 may detect thepresence of the substrate S, in step S320, and transmit this to the loadmeasuring apparatus 310. At this time, the load measuring device 311 ofthe load measuring apparatus 310 may measure a first load W1, which maybe the load of the lift device 330 before the substrate attached to theelectrostatic chuck 300 is pushed by the lift device 330, and store themeasured value in the memory 312, in step S340.

Thereafter, power may be supplied to the electrode (not shown) of thestage 351 to generate electrostatic force between the substrate S andthe electrostatic chuck 300, in step S340. The power, which may besupplied to the electrode of the stage 351, may be applied to theelectrostatic chuck 300. At this time, an electric polarizationphenomenon may be induced in the surfaces between the electrostaticchuck 300 and the substrate S. The electrostatic chuck 300 may adsorbthe substrate S using the electrostatic force generated by the electricpolarization.

After the substrate S is attached to the electrostatic chuck 300 byelectrostatic force, the power generating and transmitting device 342 ofthe drive device 340 may rotate the lift screw 341 to move the liftscrew 341 upwards. While the lift screw 341 is gradually moved upwards,the load measuring apparatus 310, which may be coupled to the lowersurface of the lift plate 332 of the lift device 330, may transmit thepressure of the lift screw 341 to the lift plate 332.

The lift plate 332, which may receive the pressure of the lift screw 341through the load measuring apparatus 310, may move upwards under theguidance of the guide bars 334 in a state in which it is parallel to thesubstrate S, and thus, move the lift pins 331 upwards. Then, the liftpins 331 may pass through the stage 351 and the chuck 300 and come intocontact with the substrate S.

At this time, the sensor(s) 302 may detect the contact between the liftpins 331 and the substrate S and transmit this to the load measuringapparatus 310. Subsequently, the load measuring device 311 of the loadmeasuring apparatus 310 may measure a second load W2, which may be theload of the lift device 330 when the substrate S is detached from thechuck 300, and store the measured value in the memory 312, in step S350.

Before the substrate S is detached from the electrostatic chuck 300,because the substrate S maintains the state in which it is attached tothe electrostatic chuck 300 by adsorbing force, electrostatic force isapplied in a direction opposite the direction in which the lift pins 331are moved upwards. Therefore, the second load W2 is the load of the liftdevice 330, including the load resulting from electrostatic force.

Further, the first load W1 and the second load W2 respectivelycorrespond to the pressure of the lift screw 341 which is applied to thelift device 330 before the lift device 330 pushes the substrate Sattached to the chuck 300, and the pressure of the lift screw 341 whichis applied to the lift device 330 in the state in which electrostaticforce is applied between the substrate S and the chuck 300.

Therefore, the electrostatic force may be calculated using the followingequation.

P=W2−W1

Here, P denotes the electrostatic force of the electrostatic chuck 300,W1 denotes a first load, which may be the load of the lift device 330before it pushes the substrate S attached to the electrostatic chuck300, and W2 denotes a second load, which may be the load of the liftdevice 330 when the substrate S is detached from the electrostatic chuck300.

Thereafter, the arithmetic device 313 of the load measuring apparatus310 may calculate the difference between the first load W1 and thesecond load W2 and determine the electrostatic force P of the chuck 300,in step S360. The display 314 may display the electrostatic force P.

In the electrostatic force measuring method according to thisembodiment, the electrostatic force P required for attaching a substrateto an electrostatic chuck may be precisely measured, so that theelectrostatic force P may be evenly applied to the electrostatic chuckin a semiconductor manufacturing process. As such, in the electrostaticforce measuring apparatus according to this embodiment and the method ofmeasuring electrostatic force, an exact value of electrostatic force maybe determined from the difference between the first load of the liftdevice 330 before it contacts the substrate S, attached to theelectrostatic chuck 300, and the second load of the lift device 330 whenthe substrate S is detached from the electrostatic chuck 300. Therefore,the exact value of electrostatic force may be applied to anelectrostatic chuck in a semiconductor manufacturing process, thuspreventing a substrate from being cracked or damaged in thesemiconductor manufacturing process, and enhancing the efficiency of thesemiconductor manufacturing process.

As described above, in an apparatus for measuring electrostatic forceand a method of measuring electrostatic force using the apparatusaccording to embodiments disclosed herein, electrostatic force may beprecisely measured, such that whether the measured electrostatic forcevalue is a value appropriate for conducting a semiconductormanufacturing process may be determined. Therefore, an error in applyingelectrostatic force during the semiconductor manufacturing process maybe prevented, so that, when the substrate is detached from anelectrostatic chuck in the semiconductor manufacturing process, thesubstrate may be prevented from being deformed or cracked.

Embodiments disclosed herein provide an apparatus and method formeasuring electrostatic force through the calculation of force appliedto a substrate when the substrate is released from electrostatic force,preventing the occurrence of an error in the determination ofelectrostatic force in a semiconductor manufacturing process, preventingthe substrate from being damaged.

An embodiment disclosed herein provides an apparatus for measuringelectrostatic force that includes a power supply unit or device thatapplies a voltage to an electrostatic chuck, a separating unit ordevices that detaches a substrate, which is attached to theelectrostatic chuck supplied with the voltage, from the electrostaticchuck, a variable load applying unit or device connected to theseparating unit, the variable load applying unit operating theseparating unit by changing a load of the variable load applying unit,and a control unit or device that measures both a load of the variableload applying unit, when the substrate is attached to the separatingunit, and a load of the variable load applying unit, when themeasurement substrate is detached from the electrostatic chuck, and tocalculate electrostatic force. The separating unit may include a vacuumunit or device that creates a vacuum to adsorb the measurementsubstrate, and a drive unit or device that transmits power to move thevacuum unit.

Further, the vacuum unit may include a vacuum suction member to adsorbthe substrate, and a vacuum pump to draw air through the vacuum suctionmember. The vacuum suction member may comprise one selected from avacuum suction pad and a vacuum suction pin.

The apparatus may further include a sensing unit or device provided inthe electrostatic chuck to detect whether the substrate is attached toor detached from the electrostatic chuck. The sensing unit may compriseone selected from a pressure sensor or a magnetic sensor. The separatingunit may include a lift unit or device that detaches the measurementsubstrate, which may be attached to the electrostatic chuck, from theelectrostatic chuck, and a drive unit or device that transmits driveforce to move the lift unit.

In addition, the lift unit may include a lift pin to contact thesubstrate to transmit the force, applied from the drive unit, to thesubstrate. A contact detecting sensor may be provided in a part of thelift pin that contacts the substrate to detect whether the lift pincontacts the substrate. The drive unit may include a power transmittingmember, which may connect the variable load applying unit to the liftunit to transmit the drive force to the lift unit.

Another embodiment disclosed herein provides an apparatus for measuringelectrostatic force that includes a chuck to seat a substrate thereon, aseparating unit or device comprising a lift unit or device that detachesa substrate from the electrostatic chuck and a drive unit or device thatoperates the lift unit, and a load measuring device that measures afirst load of the lift unit before the separating unit compresses thesubstrate and measures a second load of the lift unit when the substrateis detached from the chuck, the load measuring device calculating anelectrostatic force of the chuck using a difference value between thefirst load and the second load. The apparatus may further include asupport unit or device that supports the chuck, and may have a stageonto which the chuck is placed, and a support frame to support thestage.

The lift unit may include a plurality of lift pins to vertically movethrough the chuck and a lift plate supporting the lift pins. A sensormay be provided in the support unit to detect whether the substrate isattached to or detached from the chuck and whether the lift pins comeinto contact with the substrate.

In addition, a guide bar may be provided on the stage such that the liftplate may be slidably coupled to the guide bar, thus guiding verticalmovement of the lift unit. The drive unit may include a lift screwsupporting the lift plate, the lift screw being vertically moved, and apower generating and transmitting unit or device that rotates the liftscrew.

The load measuring device may include a load measuring unit or devicethat measures the first load and the second load, a memory unit ordevice that stores the first load value and the second load valuetherein, an arithmetic unit or device that calculates a difference valuebetween the first load value and the second load value, which may bestored in the memory unit, and a display unit or device that displaysthe difference value.

Further, another embodiment disclosed herein provides a method ofmeasuring electrostatic force that includes placing a substrate onto anelectrostatic chuck, applying a voltage to the electrostatic chuck tocharge the electrostatic chuck and attaching the substrate to theelectrostatic chuck using electrostatic force generated by the voltage,moving a vacuum unit or device upwards by changing a load of a variableload applying unit or device that detaches the substrate from theelectrostatic chuck, measuring a load of the variable load applying unitwhen the substrate is detached from the electrostatic chuck by thevariable load applying unit, and calculating a difference value betweenthe load of the variable load applying unit, measured when the substrateis detached from the electrostatic chuck, and a load of the variableload applying unit, measured when a vacuum unit or device adsorbs andholds the substrate, and determining an electrostatic force using thedifference value.

Another embodiment disclosed herein provides a method of measuringelectrostatic force that includes placing a substrate onto anelectrostatic chuck, applying a voltage to the electrostatic chuck tocharge the electrostatic chuck and attaching the substrate to theelectrostatic chuck using an electrostatic force generated by thevoltage, moving a lift unit or device upwards to detach the substratefrom the electrostatic chuck and measuring a load of a variable loadapplying unit or device when the lift unit comes into contact with thesubstrate, measuring a load of the variable load applying unit when thesubstrate is detached from the electrostatic chuck by the upwardmovement of the lift unit, and calculating a difference value betweenthe load of the variable load applying unit, measured when the lift unitcomes into contact with the substrate, and the load of the variable loadapplying unit, measured when the substrate is detached from theelectrostatic chuck, and determining an electrostatic force using thedifference value.

Another embodiment disclosed herein provides a method of measuringelectrostatic force that includes measuring a first load of a lift unitor device before the lift unit compresses a substrate attached to achuck, and measuring a second load of the lift unit when the substrateis detached from the chuck.

The method may further include attaching the substrate to the chuckusing an electrostatic force generated by applying power to the chuck,before the first measuring is conducted. In the second measuring, adifference value between the first load of the lift unit before the liftunit compresses the substrate attached to the chuck and the second loadof the lift unit when the substrate is detached from the chuck may becalculated, and an electrostatic force may be determined using thedifference value.

Any reference in this specification to “one embodiment,” “anembodiment,” “example embodiment,” etc., means that a particularfeature, structure, or characteristic described in connection with theembodiment is included in at least one embodiment of the invention. Theappearances of such phrases in various places in the specification arenot necessarily all referring to the same embodiment. Further, when aparticular feature, structure, or characteristic is described inconnection with any embodiment, it is submitted that it is within thepurview of one skilled in the art to affect such feature, structure, orcharacteristic in connection with other ones of the embodiments.

Although embodiments have been described with reference to a number ofillustrative embodiments thereof, it should be understood that numerousother modifications and embodiments can be devised by those skilled inthe art that will fall within the spirit and scope of the principles ofthis disclosure. More particularly, various variations and modificationsare possible in the component parts and/or arrangements of the subjectcombination arrangement within the scope of the disclosure, the drawingsand the appended claims. In addition to variations and modifications inthe component parts and/or arrangements, alternative uses will also beapparent to those skilled in the art.

1. An apparatus for measuring a chuck attachment force, comprising: achuck configured to receive and attach a substrate thereto; a separatingdevice that detaches the substrate from the chuck; a variable loadapplying device connected to the separating device, the variable loadapplying device operating the separating device by changing a load ofthe variable load applying device; and a controller that measures both aload of the variable load applying device when the substrate is attachedto or contacts the separating device and a load of the variable loadapplying device when the substrate is detached from the chuck, tocalculate a chuck attachment force.
 2. The apparatus of claim 1, whereinthe separating device comprises: a vacuum device that creates a vacuumto adsorb the substrate; and a drive device that transmits power to movethe vacuum device.
 3. The apparatus of claim 2, wherein the drive devicecomprises a power transmitting device that connects the variable loadapplying device to the vacuum device to move the vacuum device.
 4. Theapparatus of claim 3, wherein the power transmitting device comprises atleast one pulley and at least one power transmitting member coupled tothe at least one pulley.
 5. The apparatus of claim 4, wherein the atleast one power transmitting member comprises of a wire or chain.
 6. Theapparatus of claim 2, wherein the vacuum device comprises: at least onevacuum suction member that adsorbs the substrate; and a vacuum pump todraw air through the at least one vacuum suction member.
 7. Theapparatus of claim 6, wherein the at least one vacuum suction membercomprises one selected from a vacuum suction pad or a vacuum suctionpin.
 8. The apparatus of claim 1, further comprising: at least onesensor provided in or on the chuck to detect whether the substrate isattached to or detached from the chuck.
 9. The apparatus of claim 8,wherein at least one sensor comprises one selected from a pressuresensor, a magnetic sensor, or an optical sensor.
 10. The apparatus ofclaim 1, wherein the separating device comprises: a lift device thatdetaches the substrate from the chuck; and a drive device that transmitsdrive force to move the lift device.
 11. The apparatus of claim 10,wherein the lift device comprises at least one lift pin that contactsthe substrate to transmit the force applied from the drive device to thesubstrate.
 12. The apparatus of claim 11, further comprising: a liftplate that supports the at least one lift pin and a lift shaft thatsupports the lift plate.
 13. The apparatus of claim 11, furthercomprising: a contact detecting sensor provided in the at least one liftpin that contacts the substrate to detect whether the at least one liftpin contacts the substrate.
 14. The apparatus of claim 10, wherein thedrive device comprises a power transmitting device that connects thevariable load applying device to the lift device to transmit the driveforce to the lift device.
 15. The apparatus of claim 14, wherein thepower transmitting device comprises at least one pulley and at least onepower transmitting member coupled to the at least one pulley.
 16. Theapparatus of claim 15, wherein the at least one power transmittingmember comprises of a wire or chain.
 17. The apparatus of claim 1,wherein the chuck comprises an electrostatic chuck and the apparatusmeasures electrostatic force.
 18. A method of measuring a chuckattachment force, comprising: placing a substrate onto a chuck;attaching the substrate to the chuck using an attachment force; moving aseparating device by changing a load of a variable load applying deviceto detach the substrate from the chuck; measuring a load of the variableload applying device when the substrate is detached from the chuck; andcalculating a difference value between the load of the variable loadapplying device measured when the substrate is detached from the chuckand a load of the variable load applying device measured when theseparating device is attached to or contacts the substrate, anddetermining a chuck attachment force using the difference value.
 19. Themethod of claim 18, wherein the chuck comprises an electrostatic chuckand the attachment force comprises an electrostatic force.
 20. Themethod of claim 18, wherein the separating device comprises a vacuumdevice, wherein the moving step comprises moving the vacuum deviceupwards by changing the load of the variable load applying device todetach the substrate from the chuck, and wherein the calculating stepcomprises calculating a difference value between the load of thevariable load applying device measured when the substrate is detachedfrom the chuck and a load of the variable load applying device measuredwhen the vacuum device is attached to the substrate, and determining thechuck attachment force using the difference value.
 21. The method ofclaim 20, wherein the chuck comprises an electrostatic chuck and theattachment force comprises an electrostatic force.
 22. The method ofclaim 18, wherein the separating device comprises a lift device, whereinthe moving step comprises moving the lift device upwards to detach thesubstrate from the chuck, and wherein the calculating step comprisescalculating a difference value between the load of the variable loadapplying device measured when the lift device comes into contact withthe substrate and the load of the variable load applying device measuredwhen the substrate is detached from the chuck, and determining the chuckattachment force using the difference value.
 23. The method of claim 22,wherein the chuck comprises an electrostatic chuck and the attachmentforce comprises an electrostatic force.
 24. An apparatus for measuring achuck attachment force, comprising: a chuck configured to receive andattach a substrate thereto; a separating device, comprising a liftdevice that detaches a substrate from the chuck and a drive device thatoperates the lift device; and a load measuring apparatus that measures afirst load of the lift device before the separating device contacts thesubstrate and that measures a second load of the lift device when thesubstrate is detached from the chuck, the load measuring devicecalculating an attachment force of the chuck using a difference valuebetween the first load and the second load.
 25. The apparatus of claim24, further comprising: a support device that supports the chuck. 26.The apparatus of claim 25, wherein the support device comprises a stageonto which the chuck is placed and a support frame that supports thestage.
 27. The apparatus of claim 26, wherein the lift device comprises:at least one lift pin that vertically moves through at least onecorresponding opening provided in the chuck; and a lift plate thatsupports the at least one lift pin.
 28. The apparatus of claim 27,further comprising: at least one sensor provided on or in the supportdevice that detects whether the substrate is attached to or detachedfrom the chuck and whether the at least one lift pin come into contactwith the substrate.
 29. The apparatus of claim 28, further comprising:at least one guide bar provided on the stage such that the at least onelift plate is slidably coupled to the guide bar, wherein the at leastone guide bar guides vertical movement of the lift device.
 30. Theapparatus of claim 27, wherein the drive device comprises: a lift screwthat supports the lift plate, the lift screw being vertically movable;and a power generating and transmitting device that rotates the liftscrew.
 31. The apparatus of claim 24, wherein the load measuringapparatus comprises: a load measuring device that measures the firstload and the second load; a memory that stores a value of the first loadvalue and the second load therein; an arithmetic device that calculatesa difference value between the first load value and the second loadvalue; and a display device that displays the difference value.
 32. Theapparatus of claim 24, wherein the chuck comprises an electrostaticchuck and the apparatus measures electrostatic force.
 33. A method ofmeasuring chuck attachment force, comprising: placing a substrate on achuck; attaching the substrate to the chuck using an attachment force;moving a lift device to detach the substrate from the chuck; measuring afirst load of the lift device before the lift device contacts thesubstrate attached to the chuck; measuring a second load of the liftdevice when the substrate is detached from the chuck; and calculating achuck attachment force using the measured first and second loads. 34.The method of claim 33, further comprising: attaching the substrate tothe chuck using an electrostatic force generated by applying power tothe chuck, before measuring the first load.
 35. The method of claim 34,further comprising: determining an electrostatic force using adifference value between the first load and the second load.
 36. Themethod of claim 33, wherein the chuck comprises an electrostatic chuckand the method measures electrostatic force